import math
gamma = .5772156649015328606065120
mx = 1000000

H_table = [0] * (mx + 1)

def H(n):
	if n < 0: return 0.0
	if n <= mx: return H_table[n]
	return math.log(n) + gamma + 1 / (2 * n)

for i in range(1, mx+1):
	H_table[i] = H_table[i-1] + 1 / i

n = int(input())
ans = 0.0
i = n
while i > 0:
	v = n // i
	j = n // (v + 1)
	ans += H(v) * (H(i) - H(j))
	i = j

print(ans)